In the production of molded brake pads and other similar friction materials it was long customary to utilize granular or fibrous asbestos together with a combination of many different friction ingredients. Different combinations of ingredients in different ratios were employed to produce desired characteristics of heat resistance, friction, wear, and strength. However, asbestos is no longer favored as a component in brake pads due to its carcinogenic properties.
In the manufacture of molded brake pads that do not include asbestos, it is usually necessary to provide a combination of many more ingredients in order to obtain necessary properties in the finished product. That is, the mixtures of ingredients containing asbestos were generally simpler with respect to the number of different ingredients required. The ability of asbestos to assist in formation of a homogenous mix for ease of processing into molded brake pads was substantial.
To aid in the preparation of a mixture of raw materials having different densities, particle size and particle shape, for an asbestos-free brake pad, some manufacturers of different friction materials have used aramid fibers in pulp form. Such fibers have included the KEVLAR product of E. I. DuPont de Nemours & Co. and the TWARON product of a Netherlands company, Akzo Nobel. These aramid fiber pulps have been used in various friction materials. The pulp acts much like asbestos fiber in maintaining uniformity of the mix during processing of a molded brake pad. Other manufacturers of asbestos-free molded brake pads have employed acrylic resin pulp or mineral wool to assist in holding the mix together for processing. Reclaimed or reprocessed aramid materials have frequently been used.
The use of aramid or acrylic resin fibers, however, presents a major problem with respect to holding the complex ingredients of a brake pad together in a homogenous mixture prior to final molding of the brake pad. The aramid and acrylic fibers tend to acquire a static charge that causes them to cling to the walls of a mixer. This presents a substantial difficulty in obtaining and maintaining a homogenous final mix for the brake pad. Further, if a volatile solvent is employed, as in some liquid or semi-liquid mixtures, the static charge on the aramid or acrylic resin fibers may present a potential explosion hazard.